Waveguide mixer for radar system



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F. E. HASSELD, JR., ETAL WAVEGUIDE MIXER FOR RADAR SYSTEM 70 AFC T0 PEFFPZ-WCE P/PFAMPLIF/EE v i 249i Nov. 2, 1965 Filed April 17, 1959 DUPLEXEP I m n m M m s Rm n my m m5 0 VM W M 5 A 5 Km MM 5 WW W Y B A,

Nov. 2, 1965 F. E. HASSELD, JR.. ETAL 3,

WAVEGUIDE MIXER FOR RADAR SYSTEM 2 Sheets-Sheet 2 Filed April 17, 1959 INVENTORS F/P/I/V/(E. 66455540, JR CHAPLfS M MA) XM M ATTORNEYS United States Patent 3,215,956 WAVEGUIDE MIXER FOR RADAR SYSTEM Frank E. Hasseld, Jr., Indianapolis, and Charles W. May,

Lawrence, Ind., assignors to the United States of America as represented by the Secretary of the Navy Filed Apr. 17, 1959, Ser. No. 807,259 8 Claims. (Cl. 3339) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to a waveguide mixer and more particularly to a waveguide mixer for use in a four-lobe, monopulse, tracking radar.

Heretofore, the mixing of microwave energy has been accomplished by coupling arrangements of single rectangular waveguide conduits to provide a coupler and mixer. While this arrangement is satisfactory for single-lobe radar devices, its use in four-lobe monopulse systems results in an extremely bulky device. Furthermore, attenuators and phase shifters have to be attached to the several couplers and mixer conduits which results in a multiple number of parts.

The present invention, which relates to a mixer for a four-lobe radar system, is comprised of a single assembly having a base and cover. The base portion has a central channel therein and four channel arms connecting the central channel. Each channel arm has a short waveguide channel adjacent thereto that is separated from the channel arm by a very thin wall that has a portion removed to provide an opening into the waveguide channel. The central channel has a waveguide opening through which is transmitted microwave energy from a local oscillator. Each short waveguide channel has an opening at one end through which microwave energy is transmitted, and this energy is coupled with the local oscillator energy.

The cover portion of the mixer assembly is provided with crystal probes which extend into the various channel arms of the base portion. The cover portion is also provided with matching bends which are arranged to seat in shoulder portions in the base.

It is therefore a general object of the present invention to provide a single deck waveguide mixer for a four-lobe radar system.

Another object of the present invention is to provide a compact and light weight device for mixing microwave signals.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

FIGURE 1 is a generalized schematic view showing a mixer arrangement in accordance with the present invention;

FIGURE. 2 is a side view showing a preferred embodiment of the present invention;

FIGURE 3 is a top view showing the inside arrangement of the base portion of a preferred embodiment of the present invention;

FIGURE 4 is a top view showing the inside arrangement of the cover of a preferred embodiment of the present invention;

FIGURES is a sectional view showing an adjustable strip attenuator; and

FIGURE 6 is an enlarged sectional view showing the details of a crystal probe.

Referring now to FIGURE 1 of the drawings, it can be seen that energy from a local oscillator 11 is transmitted through channel 12 and is then evenly divided between channels 13 and 14. The energy in channels 13 and 14 passes flap-type adjustable strip attenuators 15 and 16 and then the energy in each channel is again divided into two additional channels 17 through 20. The energy in channel 17 passes through the adjustable strip attenuator 21 and is then mixed with a sample of microwave energy from magnetron 22. A pair of crystal probes 23 and 24 receive the coupled energy and after mixing in crystals the signal is transmitted to an automatic frequency control (AFC) circuit.

The other three channels, as shown in FIGURE 1 function in a similar manner. In channel 19, the energy from the local oscillator 11 is passed through the adjustable strip attenuator 25 and then mixed with microwave energy from the balanced duplexer 26. A pair of crystal probes 27 and 28 receive the coupled energy and after mixing the signal is transmitted to a reference preamplifier. In channels 18 and 20, the energy from the local oscillator 11 is passed through the variable phase shifters 29 and 30, respectively, and then mixed, respectively, with an elevation signal and an azimuth signal. The elevation signal, which is supplied by the elevation transmitting-receiving tube 31, is coupled with the energy from the local oscillator 11, and crystal probes 32 and 33 receive the coupled energy and after mixing transmit it to an elevation preamplifier. Likewise, the signal from the azimuth transmiting-receiving tube 34 is coupled with the energy from the local oscillator 11 and crystal probes 35 and 36 receive the coupled energy and transmit it to an azimuth preamplifier.

Referring now to FIGURES 2 and 3 of the drawings, it can be seen that a base 37 has the input channels attached thereto by means of screws 70. As shown, the base 37 has a central opening 38 through which energy from the local oscillator 11 enters. Grooves 39 and 40 extend in opposite directions from the central opening 38, and when the cover 10 is attached to the base 37 the central channels, which are shown as 13 and 14 in FIG- URE 1 of the drawings, are provided. Grooves 39 and 40 each divide into a T-branch at their outer ends, and these grooves and the attached cover provide channels 17 through 20. By way of example, the grooves in the base 37 may be approximately five-eighths of an inch wide and five-sixteenths of an inch deep.

An adjustable attenuator is positioned in each of the grooves 39 and 40. As shown in FIGURE 5 of the drawings, the attenuator is composed of a thin carboncoated phenolic strip 41 which is threadedly adjustable in depth. The phenolic strip 41 is cemented, or otherwise attached, to a stud 42 which is threaded on one end. The threaded end of stud 42 is engaged with a nut 43 that is fixedly attached to a housing 44. The carbon-coated phenolic strip is positioned through a slot 45 into the center of the grooves and parallel to the walls thereof. Attenuation is increased by increasing the depth of penetration of the phenolic strip into the groove.

Referring again to FIGURE 3 of the drawing, it can be seen that there are four grooves 46 through 49, that connect with the central grooves 39 and 40 and, when the cover 10 is attached, four channel arms are provided. Four short waveguide channels 50 through 53, are provided, one each being adjacent to each channel arm and separated therefrom by the thin walls 54 through 57. Each thin Wall has an opening 58 therein through which energy from the local oscillator 11 can enter into the short waveguide channels.

It should now be apparent that the energy from the local oscillator 11 enters the mixer through the central opening 38 and then divides and travels through the central channels. At the end of each central channel the energy again divides and travels through channels 17 through 20. Adjustable strip attenuators 59 and 60 are provided in channels 17 and 19, respectively, and variable phase shifters 61 and 62 are provided in channels 18 and 20 respectively. The adjustable strip attenuators 59 and 60 are comprised of a strip of carbon-coated phenolic and are slidably mounted so that their position in the channels may be changed. Maximum attenuation occurs when the strip is in the center of the channel, as the electrical field is greatest along this plane.

The variable phase shifters 61 and 62 in channels 18 and 20 are comprised of an epoxy rosin fiberglass strip which is slidably mounted so as to be positionable in the channels. The mechanism for slidably adjusting the variable phase shifters and the adjustable strip attenuators might be the same, and, by way of example might be as shown in FIGURE 3 of the drawings. A fiberglass strip 63 is supported on insulating rods 64 which in turn are attached to plate 65. A screw 66 which is threadedly attached through plate 65, has a head 67 that is held captive by the cover 68. It can readily be seen that turning of the screw 66 will cause movement of the strip 63. The adjustable strip attenuators 59 and 60 can be similarly constructed, with the only difference being that a carbon-coated phenolic strip is employed instead of the epoxy rosin fiberglass strip.

The waveguide channels 50 through 53, each have an opening through which microwave energy can enter and then be coupled with the energy from the local oscillator 11. A sample of microwave energy from the magnetron 22 enters waveguide channel 50 through opening 69 and microwave energy from the balanced duplexer 26 enters waveguide channel 52 through opening 71. Likewise, the microwave energy from the elevation transmittingreceiving tube 31 and the azimuth transmitting-receiving tube 34 enters into waveguides 51 and 53 respectively, through openings 72 and 73.

Each of the four channel arms has a restricting portion 74 and on each side of each restricting portion a reversedturn projection 75 is provided. The restricting portions 74 are provided to suppress undesirable modes of microwave energy, and the reversed-turn projections 75 are employed to match the restricting portions 74 over a wide band of frequencies. Waveguide channels 50 through 53, are also provided with restricting portions 76 and reversed-turn projections 77. As can be seen in FIGURE 3 of the drawings, the restricting portions 74 are opposite the restricting portions 76 and face one another through the openings 58 in the respective thin walls. The reversed-turn projections and the restricting portions will introduce inductive effects, producing a mismatch, and matching button 78 is used to compensate for this mismatch. The buttons 78 protrude from the broad walls of the channels and have a capacitive effect on the energy. The buttons are positioned in the center of the openings 58.

Referring now to FIGURE 4 of the drawings, there is shown a cover that is secured to the base 37 by a plurality of screws 79 that pass through clearance holes 80 and thread into the tapped holes 81 in the base 37. Four blocks 82 are adjustably attached to the cover 10 and, when the cover is assembled, these blocks 82 seat in separate shouldered portions 83 in base 37 to provide a matching bend. The adjustable blocks and their functions are more fully explained in an application entitled Matching Bend Transition, Serial Number 784,001, filed December 30, 1958, now abandoned, by one of the inventors herein, Frank E. Hasseld, Jr.

Eight crystal probes are attached to the cover 10, and also four matching buttons 84 are attached thereon. Buttons 84 are similar to the buttons 78 in the base 37, and when the cover 10 is attached to the base 37 the buttons 84 are positioned one each above the buttons 78. Buttons 84 are provided for the same purpose as buttons 78, that is, they have a capacitive effect on the energy.

The eight crystals probes serve as a means for transmitting the outputs of the mixer. FIGURE 6 shows one method of attaching the probes to the cover 10. Insulators 85 and 86 are provided to electrically insulate the metallic probes from the metallic cover 10. A nut 87 is threaded into the bore 88 to hold the insulators and probe in position. The end 89 of the probe extends into a waveguide channel and the opposite end is engageable with the connector that can be threaded into the bore 88.

In operation, the waveguide mixer is one component of a four-lobe, monopulse, tracking radar which provides airto-ground ranging capabilities, as well as azimuth and elevation tracking error signals. It is the purpose of the waveguide mixer to mix four separate signals with energy from a local oscillator. A sample of the magnetron output is applied to the automatic frequency control arm of the mixer deck and is mixed with a sample of the local oscillator output. Signals from the elevation transitting-receiving tube, azimuth transmitting-receiving tube, and the balanced duplexer are similarly combined with energy from the local oscillator 11.

It can thus be seen that the present invention provides a small compact device for mixing separate signals with a local oscillator signal with a minimum number of parts being required. Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A waveguide mixer unit comprising: an assembly of metal parts providing a plurality of enclosed channels, said channels including a central channel connecting four channel arms, and four short waveguide channels, one each paralleling each said channel arm and separated therefrom by a narrow wall; an opening in each said narrow wall providing a coupler for adjacent channel arms and short waveguide channels; means in said central channel and each said short waveguide channel for conducting microwave energy therein; and crystal probe means in each said channel arm and each said short waveguide channel for receiving the coupled microwave energy.

2. A waveguide mixer unit comprising: a base having a plurality of grooves therein; a cover removably at: tached to said base whereby a plurality of channels are provided, said channels including a central channel connecting four terminating channel arms, and four short Waveguide channels, one each paralleling each said channel arm and separated therefrom by a narrow wall; an opening in each said narrow wall providing a coupler for adjacent channel arms and short waveguide channels; means in said central channel and each said short waveguide channel for conducting microwave energy therein; and crystal probe means attached to said cover and extending one each in each channel arm and each short waveguide channel for receiving the coupled microwave energy.

3. A waveguide mixer unit comprising: a base having a plurality of grooves therein; a cover removably attached to said base whereby a plurality of channels are provided, said channels including a central channel connecting four terminating channel arms, and four short waveguide channels, one each paralleling each said channel arm and separated therefrom by a narrow wall; an opening in each said narrow wall providing a coupler for adjacent channel arms and short waveguide channels; means in said central channel and each said short waveguide channel for conducting microwave energy therein; crystal probe means attached to said cover and ex tending one each in each channel arm and each short waveguide channel for receiving the coupled microwave energy; and means in each said terminating channel arm for suppressing undesirable modes of microwave energy and for matching inductive and capacitive loads over a wide band of frequencies.

4. A waveguide mixer unit as set forth in claim 3 wherein said means in each said terminating channel arm for suppressing undesirable modes of microwave energy and for matching inductive and capacitive loads comprises: a restricting portion on the side wall of said groove and a reversed-tum projection on each side of said restricting portion.

5. A waveguide mixer unit comprising: a base having a plurality of grooves therein; a cover removably attached to said base whereby a plurality of channels are provided, said channels including a central channel connecting four terminating channel arms, and four short waveguide channels, one each paralleling each said channel arm and separated therefrom by a narrow Wall; an opening in each said narrow wall providing a coupler for adjacent channel arms and short waveguide channels; means in said central channel and each said short waveguide channel for conducting microwave energy therein; crystal probe means attached to said cover and extending one each in each channel arm and each short wave guide channel for receiving the coupled microwave energy; means in each said terminating channel arm for suppressing undesirable modes of microwave energy and for matching inductive and capacitive loads over a wide band of frequencies; means in said grooves for adjustably attenuating said microwave energy; and means for variably shifting the phases of said mcrowave energy.

6. A waveguide mixer unit as set forth in claim 5 wherein said means in each said terminating channel arm for suppressing undesirable modes of microwave energy and for matching inductive and capacitive loads comprises a restricting portion on the side wall of said groove and a reversed-turn projection on each side of said restricting portion.

7. A waveguide mixer unit as set forth in claim 5 wherein said means in said grooves for adjustably attenuating said microwave energy comprises thin carboncoated phenolic strips, and means for adjustably positioning said strips in said grooves.

8. A waveguide mixer unit as set forth in claim 5 wherein said means for variably shifting the phases of said microwave energy includes thin fiberglass strips, and means for adjustably positioning said strips in said grooves.

References Cited by the Examiner UNITED STATES PATENTS 2,574,790 11/51 King 333-10 X 2,666,134 1/54 Dicke. 2,876,421 3/59 Riblet 333 98 X HERMAN KARL SAALBACH, Primary Examiner.

CHESTER L. JUSTUS, Examiner. 

1. A WAVEGUIDE MIXER UNIT COMPRISING: AN ASSEMBLY OF METAL PARTS PROVIDING A PLURALITY OF ENCLOSED CHANNELS, SAID CHANNELS INCLUDING A CENTRAL CHANNEL CONNECTING FOUR CHANNEL ARMS, AND FOUR SHORT WAVEGUIDE CHANNELS, ONE EACH PARALLELING EACH SAID CHANNEL ARM AND SEPARATED THEREFROM BY A NARROW WALL; AN OPENING IN EACH SAID NARROW WALL PROVIDING A COUPLER FOR ADJACENT CHANNEL ARMS AND SHORT WAVEGUIDE CHANNELS; MEANS IN SAID CONTROL CHANNEL AND EACH SAID SHORT WAVEGUIDE CHANNEL FOR CONDUCTING MICROWAVE ENERGY THEREIN; AND CRYSTAL PROBE MEANS IN EACH SAID CHANNEL ARM AND EACH SAID SHORT WAVEGUIDE CHANNEL FOR RECEIVING THE COUPLED MICROWAVE ENERGY. 